Currently, the separation of compounds in a solid phase extraction (SPE) process is accomplished by vacuum and positive pressure methodologies. While automated systems exist for use with vacuum, the weakness is in that the application of vacuum is across the whole filter plate. This is because as media is pulled through a filter, the resulting compound/component cannot come into contact with anything except the well that is intended to catch the compound to eliminate potential cross contamination. For a filter plate that contains an array of wells (currently up to 384) the vacuum applied to an individual well in the array is not equal to any other well due to the resistance differences of the wells in the array as the media is filtered. Some wells in the array will pass the media through the filter faster than others and when they have completely passed the media, those wells become even less restrictive and thus allow more air to flow through subsequently reducing the amount of air flowing through the remaining wells. As a result, it is difficult to guarantee all wells have filtered their media within a given time allotment.
An additional weakness of currently known vacuum based devices is that user interaction is required in the selection and/or adjustment of adapters to set the height between the filter plate and the collection or micro plate for the purpose of engaging the nozzles of the filter plate into the wells of the collection or micro plate. The engagement is necessary to prevent possibility of cross contamination across wells. This manual process can be iterative requiring time and can be further problematic in determining the correct engagement to prevent cross contamination.
Examples of these vacuum based SPE devices are the AVS on the ML4000 and ML STAR, the CVS on the ML STAR, and the NVS on the ML Nimbus. All of these instrumentalities and systems are manufactured and sold by the assignee of the present patent application, Hamilton Company, 4970 Energy Way, Reno, Nev. 89502, United States Of America.
Positive Pressure is a solution to the problem of even flow distribution as flow restrictors can be employed to guarantee even distribution of pressure and flow to individual wells. Flow restrictors per well cannot be employed on a vacuum system as they would come into contact with the liquids being processed creating the potential for contamination. While there are positive pressure apparatus currently available, the weakness of those devices is that they are not, inter alia, friendly to automated pipetting workstations and require user interaction at virtually every stage of the SPE process as a stand-alone unit.
Hence, there is a need to overcome the significant shortcomings of the known prior-art as delineated hereinabove.